I have a 2001 EVC with about 60k miles on it.  It runs well and doesn't use oil.  It recently threw a P0172 code so I cleared it, changed the air filter and cleaned the MAF sensor.  The section of tube near the MAF sensor had a thin coating of engine oil in it.  I assume that this is from the PCV system.  Is this common or does it indicate a problem with the PCV system?